Conventional strain improvement processes are necessary to make therapeutically important polyketides commercially viable but are time consuming and tedious. The long term goals of this proposal are to develop generic approaches to polyketide overproduction and to apply these approaches to the generation of novel polyketide antimicrobials. In particular, we will target novel erythromycin analogs and cost-saving intermediates for the preparation of the ketolide class of antibiotics which have a broader range of action against MLS resistant organisms. The Specific Aims of the proposal are: i) to substitute the PKS genes in an overproducing strain with one or more heterologous PKS genes as well as low producing mutant genes and analyze the effects on polyketide production; and ii) to clone the PKS genes from an overproducer into a known S. coelicolor expression vector and compare expression to the wild-type genes in S. coelicolor. These proof-of-concept experiments will pave the way for our Phase II objectives which involve further probing of the molecular and physiological basis of polyketide overproduction and ultimately the overproduction of novel anti-microbial pharmaceuticals using well defined strains. PROPOSED COMMERCIAL APPLICATION: A generic overproducing Streptomycete host will enable production of commercially valuable antimicrobial polyketides with significant cost and time savings over existing conventional methods.